3.7. Events

Figure 3.2. A sample process using events

When you execute a process, the Rule Flow Engine makes sure that all of the relevant tasks are executed according to the process plan. It does so by requesting the execution of work items and waiting for the results. However, you can also make the rule flow respond to events that were not directly requested by the Engine. By explicitly representing these events in a rule flow, you allow yourself to specify how the process should react to them.

Each events has an associated type. It may also have associated data. You can define your own event types and their associated data.

To specify how a rule flow is to respond to events, use Event nodes. An Event node needs to specify the type of event the node is interested in. It can also define the name of a variable, which will receive the data that is associated with the event. This allows subsequent nodes in the process to access the event data and take appropriate action based on this data.

You can signal an event to a running instance of a process in these ways:

via internal events: to make an action inside a rule flow signal the occurrence of an internal event, using code like this:
```
context.getProcessInstance().signalEvent(type, eventData);
```
```
context.getProcessInstance().signalEvent(type, eventData);
```
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via external event: to notify a process instance of an external event use code like this:
```
processInstance.signalEvent(type, eventData);
```
```
processInstance.signalEvent(type, eventData);
```
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via external event using event correlation: instead of notifying a process instance directly, you can make the Rule Flow Engine automatically determine which process instances might be interested in an event using event correlation. This is based on the event type. Use this code to make a process instance that contains an event node listening for a particular external event will be notified whenever such an event occurs:
```
workingMemory.signalEvent(type, eventData);
```
```
workingMemory.signalEvent(type, eventData);
```
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You can also use events to start a rule flow. Whenever a Start node defines an event trigger of a specific type, a new rule flow instance will launch.

3.7. Events

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